1. Field of the Invention
Embodiments of the present invention relate to a matrix substrate, a detection device, and a detection system which are employed in a medical image diagnosis apparatus, a nondestructive testing apparatus, and an analysis apparatus using radiation.
2. Description of the Related Art
In recent years, a thin-film semiconductor fabrication technique has been employed in fabrication of a matrix substrate having an array (pixel array) of pixels each of which includes a combination of a switching element such as a TFT (thin-film transistor) and a conversion element such as a photoelectric conversion element and has also been employed in fabrication of a detection device and a radiation detection device employing the matrix substrate.
In recent years, a detection device employing a TFT using a polycrystalline semiconductor such as polysilicon (p-Si) has been discussed. U.S. Pat. No. 5,536,932 discloses the following content. A detection device includes a demultiplexer having a plurality of p-SiTFTs arranged between an external gate terminal having one-to-one correspondence with a terminal of an external shift register and a plurality of gate lines (driving lines) so that the p-SiTFTs correspond to the plurality of gate lines. Furthermore, the demultiplexer includes a plurality of amorphous silicon (a-Si) TFTs used to cause the gate lines to have off-state voltages of TFTs of pixels. The a-SiTFTs are constantly in an on state and cause the gate lines to maintain the off-state voltages through resistors of 1 to 5 MΩ. On the other hand, when the p-SiTFTs having resistances lower than those of the a-SiTFTs are turned on, on-state voltages are supplied to the gate lines. However, in U.S. Pat. No. 5,536,932, since the gate lines are maintained to have the off-state voltages by the a-SiTFTs, a long period of time is required until the gate lines have the off-state voltages. This is because the high resistances of the a-SiTFTs cause influence of a time constant, and accordingly, a long period of time is required until the gate lines have the off-state voltages.
Furthermore, since on-state voltages of 5 V are constantly applied to gates of the a-SiTFTs, it is highly likely that Vth shifts of the a-SiTFTs occur which is a large problem in terms of reliability.
Moreover, when this configuration is used as a substrate of a detection device, it is likely that artifact such as crosstalk is generated in signals obtained from a pixel array. Since the a-SiTFT are constantly on-states, depending on resistance values thereof, the gate lines in which the off-state voltages should be maintained may be affected by the on-state voltages from the gate lines to which the on-state voltages have been supplied through the resistors of the a-SiTFTs. In addition, when lines used to supply the off-state voltages to the a-SiTFTs intersect with data lines (signal lines), the gate lines in which influence of the off-state voltages should be maintained may be affected by potential change of the data lines through the lines used to supply the off-state voltages to the a-SiTFTs.